1. Field of the Invention
The present invention relates to a carbon fiber ball which is suitably used in the manufacture of composite materials containing carbon fibers and resin compounds containing carbon fibers, as well as a process for preparing the carbon fiber ball.
2. Background of the Invention
For the purpose of improving mechanical properties, electric characteristics, sliding performance, and other characteristics of a resin, carbon fibers are added to and compounded with the resin, and the thus-obtained composite materials have found wide utility. One known method for manufacturing such composite materials involves the continuous supply of a resin and short carbon fibers having a length of about 3-10 mm to a molding machine such as an extruder so as to attain uniform dispersion of the short carbon fibers in the resin matrix inside the molding machine, to thereby form a composite material in a continuous manner. Short carbon fibers interlaced in a complicated manner, such as pitch short carbon fibers manufactured by centrifugal spinning, are difficult to supply in quantity to a molding machine, such as an extruder, because their small bulk density prevents them from satisfactorily affording into an extruder from a hopper or from a supply means attached to a hopper. In such a case, there is employed a method in which a master batch is manufactured in advance by mixing a resin and short carbon fibers by use of a batch-type kneader, and the thus-obtained master batch is mixed with a resin to be molded. This method requires an extra step of manufacturing a master batch, and also has a drawback that continuous manufacturing cannot be performed.
In order to solve this problem, there is proposed a method in which short fibers are introduced into a swirling air stream so as to bring them to closely aggregate into a spherical shape having a diameter of 10 mm or less and a bulk density of 0.04-0.15 g/cm.sup.3 ; the resultant fibrous balls are mixed with a thermoplastic resin (powder or pellets); and then the mixture is kneaded at a temperature of not lower than the melting point of the thermoplastic resin (see Japanese Patent Application Laid-Open (kokai) No. 63-27207). However, this method is disadvantageous in that closely aggregated carbon fibers are interlaced in a complicated manner, to thereby prevent their uniform dispersion in the resin matrix during kneading.
Accordingly, the present invention is directed to a carbon fiber ball which permits a quantitative and stable supply of carbon fibers to an extruder or the like and enables the carbon fibers to be uniformly dispersed in the matrix of the resin with ease, as well as to a method of manufacturing the fiber ball.